______ is the center of our planetary system was a difficult concept to grasp in the Middle Age.
问题描述:
______ is the center of our planetary system was a difficult concept to grasp in the Middle Age.
答案是That the sun and not the earth.
为什么Being the sun and not the earth.不可以呢
不是非谓语吗,可以做为主语从句中的主语部分啊
答
动名词才可以作主语